1. Field of the Invention
The present invention relates to a position control device such as a cylinder stroke control device for controlling the stroke of the piston of a cylinder assembly, and an automotive suspension system employing such a position control device.
2. Prior art
Known automotive suspension systems employ a hydraulically operated cylinder assembly incorporated in an automobile stabilizer as disclosed in Japanese Laid-Open Patent Publication No. 61-146612, for example. When an automobile makes a turn, it is subjected to a rotating motion called "roll" about its longitudinal axis. The disclosed system eliminates the roll of the automobile by calculating a target value for the hydraulic cylinder and controlling the position of the piston in the cylinder of the cylinder assembly.
The position of the piston is detected by a potentiometer. One of the fixed and movable ends of the potentiometer is affixed to one end of the stabilizer, whereas the other potentiometer end is secured to an unsprung element. The potentiometer produces an electric signal indicative of the position of the piston in the cylinder.
According to the known suspension system, a target value for the position of the piston is calculated depending on running conditions of the automobile, and a signal representative of the difference between the target piston position and the present piston position as detected by the potentiometer is utilized for feedback control. Since the position of the piston is controlled under fluid pressure such as oil pressure, however, there is a certain response delay before the cylinder assembly is actually actuated after a control command signal is applied. Furthermore, the feedback control process requires an additional time for calculations or the like before the cylinder assembly is actually operated. Because of these time lags or delays, the driver and/or passenger or passengers of the automobile tend to feel uneasy with the attitude behavior of the automobile.
The potentiometer, which is separate from the cylinder assembly, is coupled between the stabilizer and the unsprung element. This arrangement however makes the entire suspension system relatively complex. The potentiometer itself is also complex and expensive.